sha1-file: convert pass-through functions to object_id

sha1-file: convert pass-through functions to object_id

These two static functions, read_object() and quick_has_loose(), both
have to hashcpy() their bare-sha1 arguments into object_id structs to
pass them along. Since all of their callers actually have object_id
structs in the first place, we can eliminate the copying by adjusting
their input parameters.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>